classical gland composed predominantly of cells that secrete protein hormones.
posterior pituitary (neurohypophysis) -not really an organ, but an extension of the hypothalamus. composed largely of the axons of hypothalamic neurons which extend downward as a large bundle behind the anterior pituitary. It also forms the so-called pituitary stalk, which appears to suspend the anterior gland from the hypothalamus.
TSH (also known as thyrotropin) –glycoportein consisting of:
a chain of 112 amino acids and
an chain of 89 amino acids.
The chain is identical to that found in two other pituitary hormones, FSH and LH as well as in the hormone chorionic gonadotropin.
The secretion of TSH is
-stimulated by the arrival of thyrotropin releasing hormone (TRH) from the hypothalamus.
-inhibited by the arrival of somatostatin from the hypothalamus.
As name suggests, TSH stimulates the thyroid gland to secrete its hormone thyroxine (T4). It does this by binding to GPCRs on the surface of the cells of the thyroid.
Some people develop antibodies against their own TSH receptors. When these bind the receptors, they "fool" the cell into making more T4 causing hyperthyroidism. The condition is called thyrotoxicosis or Graves' disease.
A deficiency of TSH causes hypothyroidism: inadequate levels of T4 (and thus of T3 ).
Recombinant human TSH has recently become available to treat patients with TSH deficiency.
Some people inherit mutant TSH receptors. This can result in hypothyroidism.
A deficiency of TSH, or mutant TSH receptors, have also been implicated as a cause of osteoporosis. Mice, whose TSH receptors have been knocked out, develop increased numbers of bone-reabsorbing osteoclasts.
Follicle-Stimulating Hormone (FSH)
FSH is a heterodimeric glycoprotien consisting of
- same chain found in TSH (and LH)
- chain of 115 amino acids (gives it its unique properties)
Synthesis and release of FSH is triggered by the arrival from the hypothalamus of gonadotropin releasing hormone GnRH
In adults, a hypersecretion of GH leads to acromegaly.
GH from domestic mammals like cows and pigs does not work in humans. So for many years, the only source of GH for therapy was that extracted from the glands of human cadavers. This supply was shut off when several patients died from a rare neurological disease attributed to contaminated glands.
Now, with recombinant DNA methods, recombinant human GH (rHGH) is available.
While a great benefit to patients suffering from GH deficiency, there has also been pressure to use it to stimulate growth in youngsters who have no deficiency but whose parents want them to grow up tall. Summer of 2003, the U.S. FDA approved the use of human growth hormone (HGH) for
boys predicted to grow no taller than 5′3″ and
for girls, 4′11″
even though otherwise perfectly healthy.
ACTH — the adrenocorticotropic hormone
ACTH of 39 aa peptide.
Produced from a larger precursor proopiomelanocortin (POMC).
The posterior lobe of the pituitary releases 2 hormones, both synthesized in the hypothalamus, into the circulation.
Antidiuretic Hormone (ADH). ADH is a peptide of 9 amino acids. It is also known as arginine vasopressin. ADH acts on the collecting ducts of the kidney to facilitate the reabsorption of water into the blood. This it acts to reduce the volume of urine formed (giving it its name of antidiuretic hormone).
A deficiency of ADH or
inheritance of mutant genes for its receptor (called V2)
leads to excessive loss of urine, a condition known as diabetes insipidus. The most severely-afflicted patients may urinate as much as 30 liters (almost 8 gallons!) of urine each day. The disease is accompanied by terrible thirst, and patients must continually drink water to avoid dangerous dehydration.
Oxytocin peptide of 9 aa
Acts on certain smooth muscles:
stimulating contractions of the uterus at the time of birth
stimulating release of milk when the baby begins to suckle.
Oxytocin is often given to prospective mothers to hasten birth.
Oxytocin also acts in the brain where it enhances:
bonding between males and females after they have mated;
bonding between a mother and her newborn;
and, in humans, increases the level of one's trust in other people.